An element of the abovementioned type is already known through, for example, EP 0 530 160. The element consists of a self-tapping anchoring element which is to be screwed into a hole which has been made in the jaw bone. The element is to be capable of being used in both soft and hard jaw bone. In order to achieve good primary stability even in soft bone quality, the hole is often drilled in the jaw bone using a drill which has a small diameter in relation to the anchoring element. The surrounding soft bone material is then compressed when the anchoring element is screwed in. For hard bone, larger hole diameters are used than in the case of soft bone.
In order to provide for the above mention functions, it is important that the anchoring element has good initial self-tapping properties, i.e. to make the anchoring element "make threads" in the hard surface layer, the cortical bone, which surrounds the soft bone situated within. It is therefore unacceptable, in the case of small hole diameters in the jaw bone, to use elements with none or greatly reduced thread in the front conical part because the desired initial thread engagement is then made more difficult. It is also important, however, especially in the case of hard bone, to reduce the tightening torque, i.e. that the anchoring element has an effective relief function.
The invention aims to solve the abovementioned problems and proposes an arrangement for the conical, threaded portion which on the one hand increases the effective thread area and on the other hand provides relief functions where these are most required, i.e. where the clamping is greatest.
Along the periphery on the conical portion, each thread-turn can be considered to be lowered in the locations for the relief surfaces and the recesses. The remaining thread-turn sections around the periphery must be selected optimally according to the invention to achieve an effective initial self-tapping function. The invention solves this problem.
The heights of the thread turns above their bottom plane on the conical portion of the element can also be used in order to render the initial self-tapping property more effective. The invention also solves this problem.
An anchoring element according to the invention is mainly characterized in that each relief surface is arranged on the conical portion where it extends essentially parallel to (coincides with) a plane tangential to the conical portion.
In an advantageous embodiment, the thread in the conical portion is designed so that the inner diameter of the thread is also conically arranged, i.e. the inner diameter of the thread gradually becomes smaller as the tip is approached.
In one preferred embodiment, the number of recesses, and therefore also the number of relief surfaces, is three. The three relief surfaces are parallel to or coincide with the tangential planes. Each relief surface is preferably essentially straight.
Each thread turn can be considered to consist of remaining thread-turn sections arranged at essentially the same mutual distance from one another along the periphery on the conical portion. The sector angle for each remaining thread-turn section is selected within the range 8-20.degree., preferably within the range 12-15.degree.. The sector angles for the relief surfaces correspondingly have values within the ranges of 5-15.degree. and are preferably approximately 10.degree.. Further developments of the invention emerge from the subclaims below.
The depth of the relief surfaces in the conical portion defines the sector angles for the remaining thread-turn sections for each thread turn around the periphery on the conical portion. Optimum anchoring elements can then be produced for use in both soft and hard bone. The thread turns, which are provided with increasingly lower height towards the front end of the element, contribute to an effective initial self-tapping property where good initial guidance of the anchoring element is possible even in the hard bone. The cutting of the threads into the jaw bone is reduced further at the tip of the conical portion. At the same time, the threaded surface area on the conical portion can, in total, be increased compared with the previously known elements. The relief functions are obtained where they are of greatest use by their positioning on the conical portion, which contributes to keeping the tightening torque low. This in turn reduces the risk of overstressing tools and/or damage or even locking fast in the surrounding hard bone material. It is essential that the anchoring element can be assigned the desired position or the desired optimum direction for the longitudinal axis of the element when it is screwed into the jaw bone.